The Modern Conception of the Structure and Classification of Diatoms

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by UNL | Libraries University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Papers in Systematics & Biological Diversity Papers in the Biological Sciences 5-1-1900 The Modern Conception of the Structure and Classification of Diatoms Charles E. Bessey University of Nebraska - Lincoln Follow this and additional works at: https://digitalcommons.unl.edu/bioscisystematics Part of the Botany Commons Bessey, Charles E., "The Modern Conception of the Structure and Classification of Diatoms" (1900). Papers in Systematics & Biological Diversity. 16. https://digitalcommons.unl.edu/bioscisystematics/16 This Article is brought to you for free and open access by the Papers in the Biological Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Papers in Systematics & Biological Diversity by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Transactions of the American Microscopical Society, Vol. 21, Twenty-Second Annual Meeting (May, 1900), pp. 61-86 THE MODERN CONCEPTIONOF THE STRUCTURE AND CLASSIFICATIONOF DIATOMS. WITH A REVISION OF THE TRIBES AND A RIARRANGEMENT OF THE NORTH AMJeRIOAN GENERA. BY CHARLES E. BESSEY, PH. D. WITH PLATE V. In the revision of the Bacillariaceae for Engler and Prantl's 'Pflanzenfamilien," Schiitt has availed himself principally of the stadies of Otto Miiller and has given us the first clear conception of the meaning of the diatom cell, and its relation to the diatom filament. Starting with the filament, we regard it as the typical condition, from which the unicellular diatoms have been derived by the solution of the filament and the adaptationof the separatecells to an independentlife. Diatoms are thus regarded as typically filamentous algae, and are no longer to be placed among unicellular plants. Accordingly their place in the system is readily determined,and there is no longer any excuse for tryiug to assign them to the Protophyta or Phaeophyceae, much less to place them outside the vegetable kingdom. Schiitt asserts their near relationshipto the Desmidi- aceae, and Engler in his "Syllabus der Pflanzenfamilien"assigns them to the Euphyceae, with Desmidiaceae and Zygnemaceae as close relatives on the one hand, and the Peridiniales on the other. In a recent study of the diatoms in the light of these views as to their structure, I have accepted Schiitt's interpretation with a slight modification,and have adopted the principal fea- 62 CHARLTR8 E. BESSEY tures of his classification, introducing, however, some changes in both, which I fear he may not accept. What follows must then be understood as based upon Schiitt's monograph, but with my own modifications so freely introduced that the respon- sibility for the views set forth must rest with the present writer rather than the eminent German monographer. FAMTILY BACILLARIACEAE. Cells yellowish-brown (by the addition of phycoxanthin to the chlorophyll) in unbranched filaments, circular, angled or flattened in cross section (end view or valve view); or more commonly separated early into isolated individuals (sometimes, however, more or less associated together in gelatinous colonies) which are similarly shaped, or variously twisted or bent; cell wall at first composed of cellulose, early more or less completely silicified, in most tribes very finely porous, and often wholly or partly covered with a gelatinous layer; the walls of each cell " constitute a closed box ("frustule of older authors), consisting of two ends ( " valves ") and two overlapping rings, the " girdle," and in many cases of "interzones" (zwiscbenbander), which lie between the girdle and the valves; the interzones are sometimes mere rings, but often they have more or less complete septa which transversely divide the cavity of the cell; chromat- ophores one or two, large and lamelliform, or numerous, small and granular; propagation (1) by the division of the cell (always at right angles to the axis of the filament) forming two similar cells, (2) by the escape of the protoplasm from its wall, its rapid growth into a larger cell and the formation of an en- tirely new wall (rejuvenescence), and (3) by contraction of the protoplasm of a cell and the formation of a new thick and armed wall (asexual resting spore); generation by the union of the escaped protoplasmic contents of the two cells, resulting in the formation of one or two new, usually much larger cells (several modifications of this process have been observed). Minute fresh water and marine plants, floating free or attached to vari- ous objects. CLASSIFICATION OS DIATOMS 63 The family is readily separated into two sub-families: A. SUB-FAMILY CENTRICAE.-Cells in transection circular, less commonly polygonal or elliptical, and rarely irregular; valves marked concentrically or radially by dots, areolations, lines or ribs; cells often with spines, processes or horns. B. SUB-FAMILY PENNATAE.-Cells in transection narrowly elliptical to linear, less commonly broadly elliptical, lunate, cuneate or irregular; valves marked pinnately or transversely by dots, areolations, lines or ribs; cells without spines, processes or horns (spines very rarely present, e. g., D2imerogramma and Cymatosira). Under the sub-family Centricae are arranged nine tribes, the sequence being from those which are typically cylindrical filaments to those which are flattened filaments, in the former more commonly remaining as filaments, in the latter more commonly separating into individual cells. (Plate V.) Under the sub-family Pennatae are arranged six tribes, the sequence being from those typically filamentous to those typically separated into individual cells. (Plate V.) In further interpretation of the diatom structure as indicating the relationship of these two sub-families I have regarded them as constituting two separate but somewhat parallel genetic lines, in which the Coscinodisceae and Fragilarieae are approximately primitive, the former having given rise to the Centricae and the latter to the Pennatae. In comparing the two sub-families it is interesting to note that the species of Centricae are largely marine and fossil, and those of Pennatae are largely fresh-water and recent. The structure of the plants of the former is relatively simpler, but the superficial ornamentation is usually more marked, while in the Pennatae the structure is increasingly more complex up to the Navicu'leae, Bacillarieae and Surirelleae, where the raphe is a characteristic structure, while in these the superficial ornamentation is less marked. I may say in passing that I have a similar conception of the structure of the Desmids, and that in the arrangement of the 64 OHARLES E. BESSEY families of the ConjugataeI regard the Zygnemaceaeas more nearly primitive, with their filamentous,unbranched plant-body, and that the Desmids and Diatoms represent two similar and somewhat parallel genetic lines, in which the filaments tend to break up early into independent cells, the former with a less modified cell wall, the latter with its wall usually much modified by the deposition of silica. KEY TO THE TRIBES. A. SUB-FAMILY CENTRIOAE.-Cells in transection circular, less commonly polygonal or elliptical, and rarely irregular; valves marked concentrically or radially by dots, areolations, lines or ribs; cells often with spines, processes or horns. I. Cells short box-shaped or discoid, mostly circular in transection, usually without horns or projections, a. Valves not divided into sectors by ribs, sometimes with radial rows of dots, without "eyes " (round or oval, definitely bounded, hyaline areas) or nipples, Tribe 1. Coscinodisceae. b. Valves divided into sectors by ribs, without "eyes" or nipples, Tribe 2. ActiTodisceae. c. Valves with radial undulations,or dome-shaped projections, the latter with "eyes," nipples or spines, Tribe 3. Eupodisceae. II. Cells two to many times as long as broad,circular, rarely round-ellipticalin transection; girdle with numerous interzones, Tribe 4. Solenieae. III. Cells box-shaped, about as long as broad (rarely much longer), transection circular to elliptical, with two to many horns much longer than the cell; interzones rarely present, Tribe 5. Chaetocerecae. IV. Cells box-shaped, shorter than broad or but little longer, transection circular, polygonal or commonly elliptical; valves with two (rarely one) to more poles, each pole with a projection or horn which is shorter CLASSIFICATION OF DIATOMS 65 than the cell, or when about its length provided with claws; interzones rarely present, Tribe 6. Biddulphieae. V. Cells box-shaped, as long as broad or shorter, elliptical, sometimes lunate in transection; valves without horns or projections; rarely with interzones, a. Valves lunate, without transverse septa, Tribe 7. Euodieae. b. Valves not lunate, 1. Valves with transverse septa, without spines, Tribe 8. Anauleae. 2. Valves without transverse septa, with a marginal row of spines, Tribe 9. Rutilaria. B. SUB-FAMILY PENNATAE.-Cells in transection narrowly elliptical to linear, less commonly broadly elliptical, lunate, cuneate or irregular; valves marked pinnately or transversely by dots, areolations, lines or ribs; cells without spines, processes or horns (spines very rarely present, e. g., Dimerogramrnaand Cymatosira). I. Rachis of the valves (i. e., the line between the diver- gent pinnate markings) evident as a narrowunmarked strip (pseudoraphe),rarely wanting; valve without a slit (raphe), a. Cells usually little shorter than broad or longer, with numerousinterzones, mostly united into filaments, Tribe 10. Tabellarieae. b. Cells prevailingly much shorter than broad (" rod- shaped" of older authors, the longer axis of the rod representing one of the transverse axes of the cell), often united into filaments, 1. Cells cuneate in girdle view (i. e., valves not parallel), rachis median, interzones present, Tribe 11. Meridioneae. 2. Cells rectangular in girdle view, or if cuneate the rachis not median, interzones present or absent, Tribe 12. Fragilarieae. 5 66 T ARTRES E. BESSEY II. Rachis containing an elongated slit (raphe) through the cell wall, a.

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